Continuous coupled jet-cooking/spray-drying process and novel pregelatinized high amylose starches prepared thereby

ABSTRACT

A continuous coupled jet-cooking/spray-drying process for processing inherently water-dispersible or water-soluble crystalline polymers, such as starches, polygalactomannan gums, and fully hydrolyzed polyvinyl alcohols, is disclosed. It involves the steps of: (a) forming a slurry or paste of the polymer and water, (b) jet-cooking the slurry or paste with steam at a temperature sufficient to fully disperse or solubilize the polymer, (c) immediately conveying and introducing under elevated temperature and pressure the jet-cooked dispersion or solution into a nozzle of a spray-dryer chamber, (d) atomizing the jet-cooked dispersion or solution through the nozzle, (e) drying the atomized mist within the spray-dryer chamber at a temperature sufficient to dry the polymer; and (f) recovering the dried polymer as a water-dispersible or water-soluble powder. High amylose starches (above about 40% amylose) prepared by this process are characterized in that the starch is substantially non-crystalline and substantially non-degraded. Starch mixtures, mixtures of high amylose starches and other starches, gums, or polyvinyl alcohols can be co-processed.

This application is a division of application Ser. No. 697,659, filedMay 8, 1991, now U.S. Pat. No. 5,188,674 which is a division of Ser. No.242,657 filed Sep. 12, 1988, now U.S. Pat. No. 5,131,953.

BACKGROUND OF THE INVENTION

This invention relates to a process for jet-cooking and spray-dryingwater-dispersible or water-soluble polymers, especially high viscositystarches such as high amylose starches. It also relates to the uniquepregelatinized high amylose starches produced thereby.

Pregelatinized starches (i.e., cold-water-dispersible starches) aretypically prepared by thermal, chemical, or mechanical gelatinization.The term "gelatinized" or "cooked" starch refers to swollen starchgranules which have lost their polarization crosses and which may or maynot have lost their granular structure.

The thermal processes generally used to prepare such starches includebatch cooking, autoclaving, and continuous cooking processes in a heatexchanger or jet-cooker. The thermal dispersion of a granular starch inwater involves a complex mechanism. See the discussion at pp. 427-444 inChapter 12, by Kruger & Murray of Rheology & Texture in Food Quality,Edited by T. M. DeMan, P. W. Voisey, V. F. Rasper, and D. W. Stanley(AVI Publishing, Westport, Conn. 1976), at pp. 449-520 in Chapter 21 ofStarch: Chemistry & Technology, Vol. 2, edited by R. L. Whistler(Academic Press, New York, N.Y. 1967) and at pp. 165-171 in Chapter 4 byE. M. Osman of Food Theory and Applications, edited by P. C. Paul and H.H. Palmer (John Wiley & Sons, Inc., New York, N.Y. 1972). The processbegins at the gelatinization temperature, as water is absorbed into thestarch granules, and continues as the hydrated granules swell anddisrupt into smaller granule fragments until the starch finallyapproaches a molecular dispersion. The viscosity of the cook changessignificantly during this process, increasing as the granules hydrateand swell and decreasing as the granular fragments are reduced in size.An appropriate amount of shear aids in breaking down the swollengranular fragments to give a molecular dispersion without substantialmolecular degradation.

Pregelatinized starches are typically prepared by spray-drying,drum-drying, or extrusion.

Drum-drying involves simultaneously cooking and drying a starch slurryor paste on heated, rotating drums. Cooking and drying are accomplishedover a period of time as determined by the temperature and rotation rateof the drums. The dried sheets are scraped off the drum with a metalknife and then ground. This process can be conveniently carried out athigh solids content (typically about 43% maximum). The disadvantage ofdrum-drying is that this method generally only partially disperses thestarch (i.e., the starch is not completely gelatinized) and this canresult in poorly dispersible powders having undesirable textures whenredispersed.

Extrusion may also be used to simultaneously cook and dry starches (seeU.S. Pat. No. 3,137,592 issued Jun. 16, 1964 to T. F. Protzman et al.).This method involves the physical working of a starch-water mixture atelevated temperature and pressure, causing the gelatinization of thestarch, followed by expansion during flashing off the water afterexiting from the extruder. The temperature and pressure are generated bymechanical shear between the rotating screw (auger) and cylindricalhousing (barrel) of the extruder. Cooking is accomplished with boththermal and mechanical energy as the starch is forced through thesystem. This typically results in high viscosity during processing dueto incomplete cooking and the final products are typically degraded dueto molecular breakdown caused by excessive shear. Upon redispersion, thepowders can give undesirable grainy textures, especially when lowmoisture starches are processed, due to incomplete dispersion duringcooking. When starch is processed in the presence of additional water, afurther drying step is required after the extrudate exits the extruder.This extended drying time further exaggerates the undesirable texturesupon redispersion.

The following patents describe various processes for preparingpregelatinized starches.

U.S. Pat. No. 1,516,512 (issued Nov. 25, 1924 to R. W. G. Stutzke)describes a process for modifying starch in which starch slurries areforced through a heated pipe coil and then through a spraying orificeinto a drying chamber. The slurries are processed with or without acid.The slurries are forced through the coil at excessively high pressures(e.g., 1000 lbs.) in order to insure against the possibility ofvaporizing the liquid under treatment. Steam is maintained at 35-110pounds of pressure. The temperature of the air introduced into thedrying chamber is about 121° C. (250° F.), which is reduced to about 96°C. (204° F.) at the point of evaporation. The resulting starches arehydrolyzed and are about 15-75% soluble in cold water.

U.S Pat. No. 1,901,109 (issued Mar. 14, 1933 to W. Maier) describes aspray-drying process in which starch slurries are atomized into a streamof heated air containing water vapor in such amount that vaporization ofthe water from the atomized particles occurs at a temperature above thegelatinization temperature of the starch and below the temperature atwhich further alteration (e.g., hydrolysis) occurs The process can becarried out with or without a chemical gelatinization agent.

U.S. Pat. No. 3,630,775 (issued Dec. 28, 1971 to A. A. Winkler)describes a spray-drying process in which a starch slurry is maintainedunder pressure during heating and continued under pressure through theatomization step. The pressure is interdependent with viscosity,temperature, and apparatus. The pressure requirement is that necessaryfor atomization and is in excess of that necessary to preventvaporization of water in a slurry of high solids at elevatedtemperatures. The heating time is that which is sufficient to allowsubstantially complete gelatinization and solubilization of the starchif previously ungelatinized. Typically, the slurries (10-40% solids) arepreheated to 54°-171° C. (130°-340° F.), pumped under 2,000-6,800 psi ofpressure through a continuous tubular heat exchanger, and heated to182°-304° C. (360°-580° F.)(which result in starch temperatures of163°-232° C.-325°-450° F.). Retention time of the starch in the cookeris 1.0-2.5 minutes. A conventional spray-dryer with a pressure typeatomizing nozzle is used. The resulting starches are characterized ashaving less than 12% moisture, greater than 33 lb/ft³ bulk density, andgreater than 50% cold-water solubility.

U.S. Pat. No. 4,280,851 (issued Jul. 28, 1981 to E. Pitchon et al.)describes a spray-drying process for preparing granular pregelatinizedstarches. In this process a mixture of the granular starch in an aqueoussolvent is cooked or gelatinized in an atomized state. The starch whichis to be cooked is injected through an atomization aperture in a nozzleassembly to form a relatively finely-divided spray. A heating medium isalso injected through an aperture in the nozzle assembly into the sprayof atomized material so as to heat the starch to the temperaturenecessary to gelatinize the starch. An enclosed chamber surrounds theatomization and heating medium injection apertures and defines a ventaperture positioned to enable the heated spray of starch to exit thechamber. The arrangement is such that the lapsed time between passage ofthe spray of starch through the chamber, i.e., from the atomizationaperture and through the vent aperture, defines the gelatinization timeof the starch. The resulting spray-dried, pregelatinized starchcomprises uniformly gelatinized starch granules in the form of indentedspheres, with a majority of the granules being whole and unbroken andswelling upon rehydration. Nozzles suitable for use in the preparationof these starches are also described in U.S. Pat. No. 4,610,760 (issuedSep. 9, 1986 to P. A. Kirkpatrick et al.)

U.S. Pat. No. 3,086,890 (issued Apr. 23, 1963 to A. Sarko et al.)describes a process for preparing a pregelatinized isolated amylosepowder. It involves autoclaving a slurry of an isolated amylose havingan intrinsic viscosity of 1.3-2.9 at 191° C. (375° F.) under 5-140 psigof pressure for 1-60 minutes at 0.1-25% solids, cooling the dispersionto 90° C. (194° F.) , and drum-drying on a 110°-200° C. (230°-392° F.)surface. The retention time on the drum is 40-75 seconds using a nip gapof 0.001 inch or less. The resulting powders have amorphous X-raydiffraction patterns, intrinsic viscosities of 1.3-2.9, and formirreversible gels when redispersed.

Pregelatinized starches may be made by a two step spray-drying processwhich is in current industrial use. Modifications of this conventionalprocess are described in U.S. Pat. No. 2,314,459 (issued Mar. 23, 1943to A. A. Salzburg) and U.S. Pat. No. 3,332,785 (issued Jul. 25, 1967 toE. Kurchinke). In the typical process an aqueous starch slurry iscooked, usually by atmospheric vat cooking or by cooking in a heatexchanger or by steam injection jet-cooking, held at atmosphericpressure in a tank (often a cooking tank in batch processes or areceiver tank for pressurized cooking processes), and subsequentlyspray-dried. The post-cooking holding period allows the batchwiseaddition of additives, temperature regulation, and/or cooking at rateswhich do not match the spray-dryer capacity. On exiting the holdingtanks the temperature of the feed to the spray-dryer may range from38°-93° C. (100°-200° F.). Atomization is effected by a single fluidpressure nozzle, a centrifugal device, or a pneumatic nozzle. Thisprocess is usually limited to "thin-cooking starches", i.e., convertedstarches where the polymeric structure has been degraded by acidhydrolysis, enzymatic degradation, oxidation and/or high levels ofmechanical shear. Converted starches can be used at higher solidsbecause their pastes are lower in viscosity and can be atomized. Thecooks of unmodified starches are difficult to atomize because of theirhigh viscosity and therefore, if spray-dried, are processed at lowsolids. Another limiting factor of conventional processes is that, attemperatures achieved at atmospheric pressure, many polymers associateand/or retrograde causing an increase in viscosity. See U.S. Pat. No.3,607,394 discussed below.

U.S. Pat. No. 3,607,394 (issued Sep. 21, 1971 to F. J. Germino et al.)is directed to a process for preparing a pregelatinized, cold waterdispersible starch from a granular starch which contains at least 50%amylopectin (i.e., not more than 50% amylose). Suitable starches includecereal starches such as corn, wheat and barley, tuber starches such aspotato and tapioca, and waxy starches such as waxy maize, waxy rice, andwaxy sorghum. The high amylose starches, those which contain 60% or moreamylose, as well as isolated amylose itself, are not suitable becausetheir gelling characteristics are undesirable for the applicationscontemplated (i.e., where smooth pastes having a low initial viscosityand minimal setback). The process involves pasting at at least 149° C.(300° F.), with the upper limit being that at which substantialmolecular degradation of the starch occurs, e.g., over about 232° C.(450° F.). The starch paste is then dried very rapidly in any suitableapparatus, e.g., a drum-dryer, spray-dryer, belt dryer, foam mat dryeror the like. The only requirement is that the apparatus be capable ofdrying the starch paste very rapidly to prevent retrogradation oraggregation prior to removal of the water. Also it is preferred that thepaste be fed to the dryer very quickly because the longer it is held ata high temperature the greater is the likelihood of degradation.Structurally the products are characterized by complete granularfragmentation.

It is well known that high amylose starches are especially difficult todisperse and require higher temperatures and higher shear levels thanlow amylose starches such as corn, potato, wheat, rice, tapioca, and thelike. Autoclaving or indirect heating, such as in a heat exchanger, arecooking processes that tend to produce dispersions that are complexcolloidal mixtures, especially with the difficult to disperse highamylose starches. The mixtures consist of intact granules, residualgranular fragments and dissolved polymer. Jet-cooking providesappropriate shear levels and more readily gives a dispersion approachingcomplete solubility at a molecular level (see U.S. Pat. Nos. 2,805,966(issued Sep. 10, 1957 to O. R. Ethridge); 2,582,198 (issued Jan. 8, 1957to O. R. Ethridge); 2,919,214 (issued Dec. 29, 1959 to O. R. Ethridge);2,940,876 (issued Jun. 14, 1960 to N. E. Elsas); 3,133,836 (issued May19, 1964 to U. L. Winfrey); and 3,234,046 issued Feb. 8, 1966) to G. R.Etchison). This more effective dispersion by jet-cooking provides alower in-process viscosity, without degradation, than other cookingmethods. This allows the use of lower cooking and conveying temperatureand pressure which further assists in reducing degradation.

Therefore, there is a need for a spray-drying process which convertscrystalline polymers to a substantially amorphous, i.e., "glassed" form,without substantial degradation by thoroughly cooking and dryingwater-dispersible or water-soluble natural polymers, such as unconvertedstarches and gums, or synthetic polymers such as polyvinyl alcohol atcommercially acceptable solids concentration.

There is also a long felt need for a cooking and drying process thattransforms cold-water-insoluble, partially insoluble, or slow to hydratepolymers (natural or synthetic) into new spray-dried powder forms whichdisperse in cold water and are substantially non-crystalline,non-retrograded and non-degraded by the Process. The prior art teachesmany methods that produce pre-dispersed polymers, but the resultingpolymers do not posses the full range of desired properties. There is aneed for a spray-drying process which thoroughly cooks and driescrystalline polymers, such as converted starches, at higher solids thanis currently possible.

In particular, there is a need for the following:

i) pregelatinized, spray-dried, fully pre-dispersed high amylosestarches (modified or unmodified) which disperses in water (i.e., highamylose starches which are substantially cold-water-soluble andcompletely hot-water-soluble) and whose redispersions give strong gelswith improved textural properties;

ii) fully pre-dispersed, spray-dried forms of modified or unmodifiednatural gums (which are inherently poorly dispersible due to crystallineor associated regions), especially polygalactomannan gums whosebackbones are more linear in nature and have a tendency to associate toform crystalline regions, such as locust bean gum, and whose spray-driedforms yield cold-water redispersions with the solution properties of theparent gum.

iii) fully pre-dispersed, spray-dried forms of synthetic polymers whichare inherently poorly dispersible due to crystalline or associatedregions, especially substantially fully hydrolyzed polyvinyl alcoholsand whose spray-dried forms yield cold-water redispersions with thesolution properties of the parent polymer.

SUMMARY OF THE INVENTION

The coupled jet-cooking/spray-drying process described herein is acontinuous process for jet-cooking and spray-drying an inherentlywater-dispersible or water-soluble polymer which is insoluble in coldwater because of the presence of crystalline regions and which can bedisoriented by heating, yielding a dispersion or solution which is lowin viscosity at elevated temperatures. The process comprises the stepsof:

(a) forming a slurry or a paste comprising the polymer and water;

(b) jet-cooking the aqueous slurry or paste of the polymer with steam ata temperature sufficient to fully disperse or solubilize the polymer;

(c) immediately conveying and introducing under elevated temperature andpressure the jet-cooked dispersion or solution into a nozzle of aspray-dryer chamber;

(d) atomizing the jet-cooked dispersion or solution through the nozzleof the spray-dryer;

(e) drying the atomized mist of the jet-cooked polymer within thespray-dryer chamber; and

(f) recovering the jet-cooked and spray-dried polymer as awater-dispersible or water-soluble powder.

The cooking temperature used will depend upon the polymer The use of toohigh a cooking temperature may degrade a polymer such as starch.Suitable temperatures are about 93°-177° C. (200°-350° F.) for mostpolymers, 138°-177° C. (280°-350° F.) for starches containing about 70%amylose, 121°-162° C. (250°-325° F.) for starches containing less thanabout 40% amylose, 104°-149° C. (220°-300° F.) for low viscositycold-water soluble starches, 99°-163° C. (210°-325° F.) for fullyhydrolyzed polyvinyl alcohol and 93°-163° C. (200°-325° F.) for naturalgums.

The cooking chamber pressure used in the continuous coupled process islow, typically 20 to 130 psig, and is the saturation pressure of steamat the temperature used plus the small incremental pressure needed tomove the dispersion through the chamber. Cooking chamber pressuressuitable for high amylose starches are 80 to 150 psig, most preferably100 to 130 psig for a starch having an amylose content of about 70%.

Excessive shear, like too high a cooking temperature, will degrade apolymer such as starch and should be avoided unless a converted (i.e.,degraded) starch is desired.

An essential step in the present process is the conveying of thethoroughly cooked, substantially fully dispersed polymer, under elevatedpressure and temperature, to the spray-dryer atomization nozzle. In thepreferred method, a low shear pneumatic nozzle is used, and the transferis carried out at substantially the same temperature and pressure usedin the jet-cooking. The transfer is carried out without any venting tothe atmosphere. A pressure nozzle can be used for atomization. However,its use adds operational complexity to the Process and may shear thedispersion, thus producing a degraded product.

One of the advantages of the coupled jet-cooking/spray-drying process isthat it produces a fully pre-dispersed polymer, processed withoutsubstantial degradation and dried without substantial retrogradation orreassociation, which maximizes useful properties. The spray-driedpowders redisperse in water to give dispersions with unexpected smoothtextures and high viscosities or strong gel strengths.

Another advantage of the present continuous coupled process is thathydrolyzed starches having a water fluidity (W.F.) of about 80, whichare conventionally spray-dried at 27% solids, are easily processed at38% solids. Thus, the present process is limited only by the viscosityof the feed into the jet-cooker.

A further advantage of the present process is that low solids are notrequired for proper atomization of starches of higher viscosity. Priorart conventional processes with separated cooking and spray-drying stepsare less advantageous when atomizable viscosities can only be obtainedat low solids. In those two step processes, with 70% amylose starch, thecooled starch dispersion at atmospheric pressure is too viscous tospray-dry due to retrogradation or gel formation if the solids contentof the starch slurry is above 10% solids. In the continuous coupled,jet-cooking/spray-drying process the thoroughly cooked, hot dispersionis only slightly more viscous than water, even when the solids are 25%,and hence the dispersion can be easily spray-dried.

One disadvantage of cooking the starch slurry in a tubular heatexchanger, such as that used by Winkler in the examples of U.S. Pat. No.3,630,775 (discussed in the Background) is the higher temperaturerequired since the slurry is indirectly heated rather than directlyheated as with jet-cooking. The processing conditions used by Winkler inthe high amylose starch example suggest that there were difficulties indispersing the starch since the lowest percent solids, highesttemperature and longest dwell time were used during cooking. Anotherdisadvantage is the high pressure (above 1000 psi) required to transportthe less than optimally dispersed starch through the heat exchanger andto atomize the dispersion using a single fluid pressure nozzle. A singlefluid pressure nozzle is an extremely high shear atomization devicewhich can cause molecular breakdown of high solids starch dispersions,hence altering viscosity and functionality. In contrast, in thecontinuous coupled jet-cooking/spray-drying process, the operatingpressure when the preferred pneumatic nozzle is used is less than 150psig. Atomization is thus accomplished with less shear and minimumdegradation results, thus maintaining viscosity or gelling properties ofthe original polymer. See Example XI which compares starches cooked inan heat exchanger and atomized through a single fluid pressure nozzlewith starches cooked in a jet-cooker and atomized through a pneumaticnozzle.

All of the starches which are pregelatinized using the present processcan be prepared in the form of fully pre-dispersed, non-granularstarches which are substantially non-crystalline (i.e., they areamorphous "glassed" solids). The jet-cooked dispersions are fullydispersed and do not contain granules or granular fragments; they arefully dispersed. Such pregelatinized starches are highly water-solubleand substantially non-degraded, i.e., the molecular weight of theprocessed starch is not substantially less than that of the unprocessedbase starch. When the starch base is other than a high amylose starch,such as corn, tapioca, potato, waxy maize, and the like, the resultingpregelatinized starch powder is completely cold-water-soluble (CWS).When the starch base is a high amylose starch, the resultingpregelatinized starch powder is very soluble. For example, a hybrid cornstarch having an amylose content of about 70% processed by the presentprocess has cold and hot water solubilities of about 70% and 99%,respectively. These pregelatinized high amylose starch powders give highviscosity solutions when redispersed in hot water. The split seconddrying time during processing minimizes association through hydrogenbonding so that the resulting starches are substantiallynon-retrograded.

The unique spray-dried pregelatinized high amylose starches and theirmixtures with other starches prepared by the present process form stronggels when redispersed in hot water (90°-100° C.--194°-212° F.) andcooked in a boiling water bath for 15 minutes. The gel strength is about230-240 g/cm² at 6% solids for a high amylose starch containing about70% amylose, which is equivalent to the maximum gel strength obtainedwhen the same starch is jet-cooked independently under optimum cookingconditions). Strong gels are also formed when these pregelatinizedstarches are redispersed in cold water (25° C.-77° F.) and not cooked(150-160 g/cm² at 6% solids for a high amylose starch containing about70% amylose). As is shown in Example XI, the starch is not degraded asis the starch pregelatinized using the Winkler process (see U.S. Pat.No. 3,630,775 discussed in the Background). A spray-dried starch havingan amylose content of about 70% which is pregelatinized using thepresent coupled process has an intrinsic viscosity between 0.7-0.9. Theintrinsic viscosity of the non-processed base is typically between0.9-1.0. This demonstrates that the present process produces asubstantially non-degraded starch since the molecular weight of theprocessed starch is similar to that of the base starch from which it isderived.

Typical high amylose starches include those having an amylose content ofabout 100% (e.g., isolated potato amylose) or 40-70% (e.g., cornhybrids) and the starch may be modified by derivatization, conversion,or complexing. Modification by crosslinking is possible but notdesirable as the advantage of the present process is the preparation ofsoluble starches. Lightly crosslinked starches that can be fullydispersed are suitable, whereas heavily crosslinked starches that arenot fully dispersed during cooking are not suitable.

The starches prepared by the coupled process are amorphous white powderswith particles having the shape typical of spray-dried starches, i.e. aconvoluted indented sphere. However, unlike other conventionallyspray-dried non-granular high amylose starches processed at low solids,the high amylose starch is substantially fully and completelydisorganized as evidenced by amorphous X-ray patterns, substantiallynon-retrograded as evidenced by amorphous X-ray patterns and optimum gelstrengths, and substantially non-degraded as evidenced by intrinsicviscosities that are similar to the base starch.

The high amylose starches prepared by the present coupledjet-cooking/spray-drying process are more completely dispersed thanthose prepared by the autoclaving and drum-drying process of Sarko, U.S.Pat. No. 3,086,890 (discussed in the Background). This is evidenced bythe significantly higher gel strengths. For example, the pregelatinizedstarch having an amylose content of about 70% prepared by the continuouscoupled jet-cooking/spray-drying process has a gel strength of about 160g./cm.² when redispersed in hot water at 6% solids, while the same basestarch prepared by jet-cooking and drum-drying has a gel strength ofonly about 110 g./cm.² when redispersed in hot water at 6% solids. Thisdifference in gel strength is unexpected and an indication that thecoupled continuous process produces a different product, i.e., asubstantially fully disorganized and non-retrograded product. Theautoclaving and drum-drying process of Sarko uses, as a startingmaterial, a previously processed starch fraction (isolated amylose)which is prepared by high temperature cooking, precipitation of thedesired fraction, and recovery by drying. In the present process,isolated starch fractions are usable, but native (non-cooked) starchesare preferred.

The high amylose starch powders prepared by the coupledjet-cooking/spray-drying process are significantly more dense thanpregelatinized starches prepared using a conventional two step processwhich involves jet-cooking and then spray-drying a low solids aqueousdispersion of the jet-cooked starch, as shown in example XIII anddiscussed in Example XIV. The high amylose starch powders obtainedherein also form a significantly firmer gel (about 200 versus 45-90g./cm.² at 6% solids when redispersed in hot water).

The high amylose starch powders and other starch powders prepared by thecoupled jet-cooking/spray-drying process are completely non-granularunlike the pregelatinized starches prepared by cooking the starch in anatomized state. As described in U.S. Pat. No. 4,280,851 (discussed inthe Background), the simultaneously cooked and spray-dried starches areuniformly gelatinized granules in the form of indented spheres with amajority of the granules being whole and unbroken and swelling uponrehydration. In attempting to carry out this process with a high amylosestarch (about 70% amylose), we have observed that it is difficult toprepare a highly soluble product. The high amylose starch is resistantto gelatinization under the processing conditions described in thisreference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the high temperature viscometer, a measurement device usedto carry out the high-temperature flow rate viscosity measurement.

FIG. 2A shows a X-ray crystallographic scan for a high amylose starch(about 70% amylose) pregelatinized by the present continuous coupledjet-cooking/spray-drying process.

FIG. 2B shows a X-ray crystallographic scan for a high amylose starch(about 70% amylose) pregelatinized by jet-cooking and drying on a heatedplate.

FIG. 2C shows a X-ray crystallographic scan for a high amylose starch(about 70% amylose) pregelatinized by jet-cooking and air-drying (seeCurve C).

FIG. 3 compares the gel strengths of spray-dried high amylose starches(about 70% amylose) pregelatinized using the present continuous, lowshear, direct heating process which couples a jet-cooker with aspray-dryer having a pneumatic-type nozzle and the cook of thecontinuous, high shear, indirect heating process exemplified by Winklerin U.S. Pat. No. 3,630,775 which couples a tubular heat exchanger and aspray-dryer using a single fluid high pressure nozzle.

FIG. 4 compares the viscosities of waxy corn starch, pregelatinizedusing the present continuous, low shear, direct heating process whichcouples a jet-cooker with a spray-dryer having a pneumatic-type nozzle,and the cook of the continuous, high shear, indirect heating processexemplified by Winkler in U.S. Pat. No. 3,630,775 which couples atubular heat exchanger and a spray-dryer using a single fluid pressurenozzle.

FIG. 5 compares the viscosities of corn starch pregelatinized using thepresent continuous, low shear, direct heating process which couples ajet-cooker with a spray-dryer having a pneumatic-type nozzle and thecook of the continuous, high shear, indirect heating process exemplifiedby Winkler in U.S. Pat. No. 3,630,775 which couples a tubular heatexchanger and a spray-dryer using a single fluid high pressure nozzle.

FIG. 6A presents scanning electron microscope photomicrograph of thefully dispersed, non-granular pregelatinized high amylose starchprepared by the continuous coupled jet-cooking/spray-drying process.

FIG. 6B presents a scanning electron microscope photomicrograph of thegranular, spray-dried particles of pregelatinized high amylose starchprepared by the simultaneous atomization and cooking process of Winkler(U.S. Pat. No. 4,280,851).

FIG. 6C presents a scanning electron microscope photomicrograph thepregelatinized high amylose starch prepared by thejet-cooking/drum-drying, a process similar to that of Sarko (U.S. Pat.No. 3,086,890).

FIG. 7 compares the displacement density and bulk density of variouspregelatinized starches (potato amylose, high amylose corn, Potato,corn, tapioca and waxy maize) prepared by the continuous coupledjet-cooking/spray-drying process, a conventional spray-drying process,and the jet-cooking/drum-drying, a Process similar to that of Sarko(U.S. Pat. No. 3,086,890).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term "crystalline" polymer refers to any natural orsynthetic polymer which contains crystalline regions or domains whichmust be disorganized to render the polymer amorphous and hencedispersible or soluble in cold water. Suitable polymers for use in thepresent process are those which develop a high viscosity afterdispersion in hot water and whose aqueous dispersions have a reducedviscosity at elevated temperatures. Suitable natural polymers includewater-dispersible or water-soluble polysaccharides such as starches,gums and cellulose derivatives. Suitable synthetic polymers includepolymers such as fully hydrolyzed, medium to very high molecular weightpolyvinyl alcohols.

Any cookable, granular unmodified or modified starch or previouslycooked starch (including those not fully dispersed) other than a highlycrosslinked starch is suitable as a starting material for use in thepresent process. Different types of suitable base starches include thosefrom cereal grains, such as corn, milo, wheat and rice; those fromtubers, such as potato, tapioca, and arrowroot; and those that are waxystarches, such as waxy milo, wavy maize, and waxy rice.

As used herein, the term "high amylose starch" refers to starches fromany starch base which contain concentrations of at least about 40%amylose, including, for example, high amylose corn, wrinkled pea, and100% amylose isolated from a starch such as potato starch. It alsorefers to mixtures of a high amylose starch and starches having anamylose content below 40%, such as waxy maize, corn, tapioca, potato,rice and the like. The mixtures can be processed and yield a mixedpowder with good gelling properties, provided the mixture has a totalamylose content of at least 35%. The preferred high amylose starches arethose derived from high amylose corn hybrids.

Jet-cooking is a conventional process which involves the instantaneousheating of a flowing liquid (in the present process an aqueoussuspension, also referred to as a slurry or paste) with a hotcondensable vapor (in the present process steam) and holding the heatedliquid at a selected temperature for a selected time. Various apparatussuitable for jet-cooking are referred to in the Background. Suitablecookers are available from National Starch and Chemical Corp. (UnitedStates), Avebe (Holland), or Roquette Freres (France).

Spray-drying is likewise a conventional process and described in SprayDrying: An Introduction to Principles, Operational Practice andApplications by K. Masters, published in 1972 by Leonard Hill Books, adivision of International Textbook Co Ltd., London. Spray-dryer nozzlessuitable for use herein include pressure nozzles and pneumatic-typenozzles such as two-fluid nozzles.

In a pneumatic nozzle, the liquid to be atomized (here the cookedpolymer dispersion) and an atomizing gas (air or steam) are fedseparately to the nozzle at pressures generally between 50 psig and 200psig. Atomization is effected by impinging the pressurized atomizing gason a stream of the liquid at a velocity sufficient to break the streaminto droplets. In the present invention, pressure (and the resultingvelocity) of the atomizing as must be sufficient for propert atomizationinto small droplets to allow rapid drying to an appropriate residualmoisture without retrogradation or reassociation. Use of pneumaticnozzles is preferred in the coupled jet-cooking/spray-drying process dueto the low operating pressures (similar to those needed for jet-cooking)and the low shear on the feed inherent in this design. Pneumatic nozzlesare discussed in greater detail on pages 16 f of Master's book citedabove.

Pressure nozzles may also be used for atomization. Atomization, in apressure nozzle, is effected by inducing rotation in the liquid andpassing it through a small orifice. The liquid, on exiting the orifice,forms a cone-shaped film which is unstable, breaking into droplets. Useof a pressure nozzle in the present process requires insertion of a highpressure pump (2,000 to 10,000 psig) between the jet-cooker and theatomization nozzle. The temperature after passage through the highpressure pump should be maintained substantially equivalent to thejet-cooking chamber temperature. The pressure after the high pressurepump must be sufficient to properly atomize the dispersion into smalldroplets to allow rapid drying to an appropriate residual moisturewithout retrogradation or reassociation. Use of a pressure nozzle addsoperational complexity to the present process and may shear thedispersion, thus producing a degraded product. Suitable pressure nozzlesare also described in the Masters reference cited above.

For example, in the present process a starch slurry (up to 38% anhydrousbasis) is prepared. The starch slurry is then directed through a cookingchamber, mixed with high temperature steam (at 80-150 psig), andgelatinized in a continuous jet-cooker. The starch is cooked at a solidsand temperature sufficient to reduce its viscosity at elevatedtemperature to a low range (near that of water), without significantdegradation.

The exit of the cooking chamber is connected to a spray-nozzle,preferably a pneumatic-type spray-nozzle, situated in a spray-dryer. Thestarch cook, while still at a high temperature and low viscosity, isdirected into the spray-nozzle and atomized with cold air, hot air orsteam. Once the hot jet-cook has been atomized, it is handled in thesame manner as conventional spray-dried starches.

The continuous coupled process is economical. It provides high flowrates through a given spray-dryer orifice at high starch solids but atpressures that are low enough to minimize degradation of the starch.

The coupled process is versatile. The processing equipment may bearranged to optionally add other materials during the jet-cooking step.For example, (1) a water-soluble compound such as sugar or awater-dispersible compound such as a gum can be added to a starch slurryand a spray-dried mixed powder obtained; (2) a water-insoluble compound,such as an oil, can be added to the starch and a starch powdercontaining encapsulated oil obtained; (3) a complexing agent such as asurfactant can be added to a starch slurry and a starch-surfactantcomplex obtained; (4) an acid may be added to the slurry and anacid-converted starch product obtained; or (5) a derivatizing agent maybe added to the slurry and a derivatized starch product obtained. Theprocessing equipment can also be arranged to provide for post-dryingtreatments such as the agglomeration of the starch powder, or aheat-moisture treatment of the starch powder.

The above procedure (encapsulation, complexation, conversion,derivatization, agglomeration, and heat treatment) are well-known starchmodifications and described, for example, in Chapter 22: Starch and ItsModification by M. W. Rutenberg in Handbook of Water-Soluble Gums andResins, edited by Robert L. Davidson and published by McGraw Hill BookCo., New York 1980 or in the patent literature.

Jet-cooks of a high amylose starch (about 70% amylose) maintained attemperatures from 126°-153° C. (259°-307° F.) flow through spray-dryingnozzles at rates no less than half that of water, even at a 28% cooksolids. This translates into a flow viscosity of less than 1 centipoiseat temperatures of 109°-145° C. (228°-293° F.). The viscosity of a 28%solids jet-cook of the same starch cannot be measured after it exits thecooker and drops in temperature to below 100° C. (212° F.) since itforms a gel in a few seconds. Therefore, flow rates are measured insteadof viscosity. Accurate viscosity measurements of non-Newtonian liquidssuch as starch cooks are very difficult to measure.

Starch cook viscosities (by flow rate comparison with water) decreasewith increasing temperature, decreasing molecular weight, decreasingsolids, and increasing amylose content (e.g., a high amylose starchhaving an amylose content of about 50% is more viscous than a highamylose starch having an amylose content of about 70%).

In the examples which follow, all temperatures are in degrees Celsuisand Fahrenheit. All spray-drying nozzles are obtainable from SpraySystems Co., Wheaton, Ill. The following test procedures were used.

WATER SOLUBILITY A. Cold Water Solubility

The determination is carried out using distilled water at roomtemperature. About 0.5 g. of starch is dispersed in 30-40 ml. of waterin a semi-micro stainless steel cup on a Waring blender base (Model31B292). The blender is run at low speed while the starch is added (allat once) and then run at high speed for 2 minutes. The dispersion isimmediately transferred to a 50 ml. volumetric flask and diluted to 50ml. with water. A 25 ml. portion of the stock dispersion (shaken well toensure a homogenous dispersion) is removed by pipet and transferred to a50 ml. centrifuge tube. The sample is spun down at 1800-2000 RPM for 15minutes. Once spun down, 12.5 ml. of supernatant is pipetted into a 25ml. volumetric flask, 5 ml. of 5N potassium hydroxide (KOH) are addedwith swirling, and the mixture is diluted with water. The remainder ofthe stock dispersion is shaken well, the insoluble starch dispersed with10 ml. of 5N KOH while swirling. The mixture is diluted to 50 ml. withwater. The optical rotation of both the concentrated stock solution (B)and the supernatant solution (A) is measured. ##EQU1##

B. Hot Water Solubility

The procedure is the same as that described above except that boilingdistilled water at 90°-100° C. (194°-212° F.) is used for dispersing thestarch and all subsequent dilutions. No attempt is made to maintaintemperature during the procedure.

FLUIDITY MEASUREMENTS A. Water Fluidity (W.F.)

This test is described in U.S. Pat. No. 4,207,355 issued Jun. 10, 1980to C. W. Chiu et. al., the disclosure of which is incorporated herein byreference.

B. Calcium Chloride Viscosity (7.2% Solids Test)

The calcium chloride viscosity of the converted high amylose starch ismeasured using a Thomas Rotation Shear-Type Viscometer standardized at30° C. (86° F.) with a standard oil having a viscosity of 24.73 cps.,which oil requires 23.12±0.05 seconds for 100 revolutions. As theconversion of the starch increases, the viscosity of the starchdecreases and the calcium chloride viscosity decreases. Accurate andreproducible measurements of the calcium chloride viscosity are obtainedby determining the time which elapses for 100 revolutions at a specificsolids level.

A total of 7.2 g. of the converted starch (anhydrous basis) is slurriedin 100 g. of buffered 20% calcium chloride solution in a coveredsemi-micro stainless steel cup (250 ml. capacity available fromEberbach), and the slurry is transferred to a glass beaker and is heatedin a boiling water bath for 30 minutes with occasional stirring. Thestarch solution is then brought to the final weight (107.2 g.) with hot(approximately 90°-100° C.--194°-212° F.) distilled water. The timerequired for 100 revolutions of the resultant solution at 81°-83° C.(178°-181° F.) is measured three times in rapid succession and theaverage of the three measurements is recorded.

The calcium chloride solution is prepared by dissolving 264.8 g. ofreagent grade calcium chloride dihydrate in 650 ml. of distilled waterin a tared 1 l. glass beaker. Thereafter 7.2 9. of anhydrous sodiumacetate is dissolved in the solution. The solution is allowed to cooland the pH is measured. If necessary, the solution is adjusted withhydrochloric acid to pH 5.6±0.1. The solution is then brought to weight(1007.2 g.) with distilled water.

GEL STRENGTH

A gel is prepared by dispersing a starch sample (on an anhydrous basis)in boiling distilled water (approximately 90°-100° C.--194°-212° F.) atappropriate solids in a Waring blender (Model 31B292) set at low speedfor 2 minutes, transferring to a glass beaker, then cooking the samplein a boiling water bath for 15 minutes. The sample is brought back toweight with boiling distilled water and is then placed in a jar coveredwith a lid and allowed to cool undisturbed for 24 hours at 21° C. (70°F.) to gel. Unless stated otherwise, all gels are prepared in boilingwater and cooked as stated above. For cold water gel strengths, the gelis made in room temperature (25° C.--77° F.) distilled water withoutcooking. The strength is measured using a Stevens LFRA Texture Analyzer(available through Texture Technologies Corp , Scarsdale, N.Y.)employing a 0.25 in. diameter cylindrical probe, run at a speed of 0.5mm./sec. The force in g./cm.² required for the probe to penetrate thegel a distance of 4 mm. is measured three times and the average isrecorded. The solids and probe selection are varied according to thestarch type. For example, all high amylose corn starches (about 70%amylose) and isolated potato amylose (about 100% amylose) were testedwith a 0.25 in. diameter cylindrical probe at 6% solids (dry basis).Unless stated otherwise, these conditions can be assumed.

BROOKFIELD VISCOSITY

Brookfield viscosity is measured using a RVF Brookfield viscometer(available through Brookfield Engineering Laboratories, Inc., Stoughton,Mass.) and an appropriate spindle at 20 rpm. The instrument is allowedto rotate five times before a reading is taken. All viscosity readingsare run at 22° C. (72° F.), and all test dispersions are prepared usingthe above gel strength procedure unless stated otherwise.

INTRINSIC VISCOSITY DETERMINATION

The intrinsic viscosity of starch is measured by quantitativelytransferring 2.500 g.±0.001 g. of anhydrous starch into a 600 ml. beakercontaining about 250 mls. of distilled water at about 25° C. (77° F.).Then 100 mls. of 5N±0 05N KOH solution are pipetted into the beaker, andthe mixture is stirred for 30 minutes on a stir plate. This solution isclear and does not contain undissolved starch. The flask and is broughtto volume with distilled water. The solution is quantitativelytransferred to a 500 ml. volumetric solution is filtered through afunnel packed with glass wool. Then 40.0, 30.0, 20.0 and 10.0 mls. ofthis solution are pipetted into 50 ml. volumetric flasks and brought tovolume with 1N±0.10N KOH solution. The flow times for each concentration(0.40, 0.30, 0.20 and 0.10% solids plus the stock solution at 0.50%solids) and the flow time of the 1N KOH solution is determined in aCannon-Fenske Viscometer (No. 100, 45-65 seconds flow time for water at35° C.) mounted in a constant temperature bath maintained at35.00°±0.02° C. The flow times for each dilution are run in triplicate.The intrinsic viscosity is the point at which the extrapolated line of aplot of N_(sp) /concentration (y-axis) versus concentration (x-axis)intercepts the y-axis. N_(sp) =N_(rel) -1 and ##EQU2##

VISCOSITY BY FLOW-RATE MEASUREMENT

The device used for high-temperature flow-rate viscosity measurement isshown in FIG. 1. It is used to measure the flow rate of fluids underhigh temperature/pressure conditions. A jet-cooker is used to raise thetemperature/pressure of these fluids. The high temperature starch cookviscosity is determined by comparing its flow rate to that of waterunder identical conditions. Solids concentration are stated in theExamples.

The "small" nozzle orifice, which has an opening of 0.016 in., is usedfor low solids cooks (spraying systems fluid cap 40100). The "large"nozzle orifice, which has an opening of 0.031 in., is used for highsolids cooks (fluid cap 600100).

A. Cooked Starch Flow Rate Measurement

The starch is slurried in water at the desired solids and adjusted toapproximately pH 6 with dilute sulfuric acid or sodium hydroxide asrequired. The slurry is then jet-cooked at temperatures between149°-155° C. (300°-311° F.). The starch cook is then directed (whilekept at temperature) into an insulated steel chamber fitted with aspray-drying nozzle and an overflow line to flash off excess steam andto control pressure. The valve opening to the overflow line is adjustedto bring the pressure and thus the temperature to the desired point andto eliminate any excess steam. Gases (steam) in the liquid stream causean uneven flow ("spitting") and must be eliminated to provide accurateflow results. Once the pressure/temperature have been adjusted and steamhas been eliminated, a valve is opened to allow flow through thespray-drying orifice while maintaining constant pressure.Simultaneously, a graduated cylinder is placed under the orifice and atimer is started. A sample is collected for approximately 30 seconds,from which the flow rate per minute is calculated. Water is run throughthis procedure and is used as the standard for comparison.

B. Water Flow Rate Measurement

Water was run at 20, 40 and 60 psig of pressure to obtain temperaturesof 126°, 142°, and 153° C. (259°, 287°, 307° F.) using the proceduregiven above. The results are shown below:

    ______________________________________                                        Orifice             Temperature                                                                              Flow                                           Size    Pressure    of Fluid   Rate                                           (in.)   (psig)      °C. (°F.)                                                                  (ml./minute)                                   ______________________________________                                        0.016   20          126 (259)  100                                            0.016   40          142 (287)  138                                            0.016   60          153 (307)  180                                            0.031   20          126 (259)  360                                            0.031   40          142 (287)  600                                            0.031   60          153 (307)  699                                            ______________________________________                                    

POWDER DENSITY A) Bulk Density

A tared 100 cc. graduated cylinder is filled to the 100 cc. mark with"as is" test sample powder. The cylinder is tapped on a hard surfaceuntil no further drop in volume is noted. ##EQU3##

B) Displacement Density

A Hubbard-Carmick, 25 ml. capacity, specific gravity bottle is tared anda small amount of anhydrous glycerin is added to wet out the bottom ofthe bottle. A known amount of starch (about 5 g. "as is") is weighedinto the bottle and the bottle is filled about half way with moreglycerin. After mixing, the bottle is filled within 1/4 to 1/8 inch ofthe top with glycerin and placed under a vacuum until all air bubblesare dissipated. Glycerine is added to completely fill the bottle and thetotal weight is taken. The procedure is run with glycerin alone (nostarch) to determine the volume of the bottle. All work must be done at25° C. (77° F.). ##EQU4##

EXAMPLE I

This example shows the preparation of pregelatinized non-granular highamylose corn starches (about 70% amylose).

PART A--PREPARATION AT LOWER COOK SOLIDS (13%)

An unmodified granular high amylose starch was slurried in water andpumped using a gear pump into a jet-cooker. Steam (at 145 psig) wasmetered into the slurry stream and the starch was cooked. The hot starchcook was conveyed at a temperature and pressure only slightly reducedfrom the cooking chamber to a pneumatic atomization nozzle bottommounted in a spray-dryer. Compressed air was used to atomize the starch.Hot air in counter-current flow was used to dry the atomized starchmist. The resulting powders were recovered in a cyclone separator. Theprocess variables used are shown in Table I. The spray-dryer is alaboratory Model No. 1 Anhydro spray-dryer.

The effect of cooking shear on the gel strength of starch powdersredispersed at 6% solids in hot water is shown. The shear was varied byvarying the amount of gaseous steam present in the starch cook as itmoved through the cooker. At lower shear levels (20.0 g./min. of steamflow), the starch was not thoroughly and efficiently cooked, and thiswas reflected in less than maximum gel strength (194 g./cm.²) (seeColumn 1). At optimum shear levels for this system (24.0 g./min. steamflow) a maximum gel strength of 215 g./cm.² was achieved. Increasing theshear by using a steam flow of 36 or 62 g./min. resulted in lower gelstrengths (204 and 134 g/cm.²) (see columns 3 and 4). Proper shear mustbe determined experimentally and it will depend on the starch used, thehydraulic characteristics of the cooking and atomizing equipment used,and the cooking temperature, as well as the gel strength required forthe desired end use.

PART B--PREPARATION AT HIGHER COOK SOLIDS (28%)

The process variables used for jet-cooking/spray-drying in larger scaleequipment at higher solids are shown in Column 5 of Table 1. The slurryof unmodified granular high amylose starch was fed into a jet-cooker(Model C-15 available from National Starch and Chemical Corp). Steam wasmetered into the slurry as above. The cooked starch was conveyed to apneumatic atomization nozzle top mounted in a 35 ft. tall, 16 ft.diameter Hensey spray-dryer. Steam at 120 psig was used to atomize thestarch. The atomized starch mist was dried with air at 204° C. (400°F.).

The cold water solubility of the above non-granular starch powders was97.4% and the hot water solubility was greater than 99%.

The types of pneumatic nozzle set-ups used in the spray-dryers areindicated in the Table and available from Spraying System Inc.

EXAMPLE II

This example demonstrates the processing of a converted high amylosecorn starch (about 70% amylose) using the coupledjet-cooking/spray-drying process. A slurry of the starch was treatedwith 2.5% hydrochloric acid at 52° C. (126° F.) for 16 hours to give aconverted starch having a calcium chloride viscosity of 25 seconds.After neutralization with sodium carbonate to a pH of about 6, thegranular converted starch was filtered, washed and dried. The starch wasthen jet-cooked using the following conditions: 21% cook solids, 143° C.(290° F.) cooking temperature, 27 g./min. steam flow, and 39.7 ml./min.cooking rate. The jet-cooked starch dispersion was spray-dried through atwo-fluid Spray Systems nozzle (set-up 22) into a Niro Utility #1spray-dryer. The inlet temperature was 250° C. (428° F.) and the outlettemperature was 88° C. (190° F.) The starch powder was 93.0% soluble incold-water and 97.1% soluble in hot-water.

EXAMPLE III

This example demonstrates that a blend of a high amylose corn starch andanother starch can be processed using the coupledjet-cooking/spray-drying process. About 35 parts of a converted highamylose corn starch (about 70% amylose and calcium chloride viscosity ofabout 25 seconds) was slurried with about 65 parts of a converted cornstarch (about 28% amylose and water fluidity of 65) in 150 parts ofwater. The following jet-cooking conditions were used: 23% cook solids,143° C. (290° F.) cooking temperature, 27.5 g./min. steam flow, and 39ml./min. cooking rate. The jet-cooked starch dispersion was spray-driedthrough a two-fluid Spray Systems nozzle (set-up 22B) into an Anhydrolaboratory Model No. 1 spray-dryer. The inlet temperature was 230° C.(446° F.) and the outlet temperature was 86° C. (187° F.) .

The resulting non-granular starch powder was 95.1% soluble in cold waterand greater than 99% soluble in hot water. On redispersion in hot waterat 6% solids it formed a gel having a strength of 42 g./cm.². Thefluidity corn starch processed under similar conditions did not gel. Thefluidity high amylose corn starch processed under similar conditionsformed a gel having a strength of 75-85 gm./cm.². The results show thatthe co-processed blend provided a starch powder which formed a gel.

EXAMPLE IV

This example demonstrates that a mixture of a granular unmodified highamylose corn starch (about 70% amylose) and fructose or sorbitol can beprocessed using the coupled jet-cooking/spray-drying process.

The processing conditions and results were as follows:

    __________________________________________________________________________                   Typical High                                                                          87.5% High                                                                            92.5% High                                                    Amylose Amylose Amylose                                                       Starch  Starch + 12.5%                                                                        Starch + 7.5%                                  Conditions     (Comparative)                                                                         Fructose                                                                              Sorbitol                                       __________________________________________________________________________    Cook solids (%)                                                                              15-16   14.5    14.0                                           Cooking temperature (°C.(°F.))                                                 143 (290)                                                                             143 (290)                                                                             143 (290)                                      Steam flow (g./min.)                                                                         27.5    27.5    27.5                                           Cooking rate (ml./min.)                                                                      24-36   35.0    35.0                                           Spray-dryer    Anhydro Anhydro Anhydro                                        Inlet temperature (°C. (°F.)                                                   240 (464)                                                                             220 (428)                                                                             230 (446)                                      Outlet temperature (°C. (°F.)                                                  90 (194)                                                                              82 (180)                                                                              84 (183)                                       Two fluid nozzle set-up                                                                      22B     22B     22B                                            Cold water solubility (%)                                                                    71.4    64.9    96.6                                           Hot water solubility (%)                                                                     94.5    83.7    80.3                                           Gel strength at 6% solids                                                                    220     119.0   172.0                                          (g./cm..sup.2)                                                                __________________________________________________________________________

The results show that co-processed powdered mixtures were highly soluble(64.9 and 96.6%) in cold water and formed strong gels (119 and 172g./cm.²) even though they contained lower starch solids than thecomparative sample.

EXAMPLE V

This example describes the production and recovery of a derivatizedstarch using the coupled jet-cooking/spray-drying process.

A starch is slurried in water and the pH is adjusted to between pH 6 andpH 8 with sulfuric acid or sodium hydroxide as required. An aqueoussodium tripolyphosphate (STP) solution is added either to the bulkstarch slurry or metered into the starch feed line prior to thejet-cooker at a level sufficient to give 1 to 4% STP on starch. Thestarch/STP slurry is jet-cooked at a temperature 163°-177° C. (325°-350°F.).

This modified starch dispersion is conveyed, at temperature and pressuresubstantially equivalent to those used during cooking directly to anatomization nozzle mounted in a spray-dryer. After atomization anddrying the resulting powder is collected.

It is expected that the recovered starch powder will have the propertiesof a conventional starch phosphate produced by slurry reaction. Inaddition, it is expected that the powder will be readily water-solubleand not require cooking to produce a functional water dispersion.Reactions on cooked starches are known but yield liquid Products andhave generally been avoided due to difficulty in recovering the viscousreaction products or expense in recovering low solids cooks. Forexample, U.S. Pat. No. 3,637,656 (issued Jan. 25, 1972 to F. J. Germinoet al.) and U.S. Pat. No. 4,579,944 (issued Apr. 1, 1986 to R. G. Harveyet al.) describe paste reaction processes for making starch derivatives.

EXAMPLE VI

This example shows that other granular high amylose corn starches can bejet-cooked and spray-dried using the coupled process. The processingconditions used for fractionated Potato amylose (about 100% amylose),unmodified high amylose corn starch (about 50% amylose), and convertedhigh amylose corn starch (about 70% amylose and having a calciumchloride viscosity of 25 seconds) are shown in Table II.

The results show that the non-granular powders are highly soluble incold water (86.6, 95.3, and 93.0%, respectively) as well as in hot water(99.2, 96.9, and 97.1%). They form strong gels (395, 125 and 104 g/cm²,respectively).

EXAMPLE VII

This example demonstrates the use of the coupled jet-cooking/spray-drying process to prepare a cold-water-soluble form of acold-water insensitive synthetic polymer.

A medium molecular weight fully hydrolyzed polyvinyl alcohol (availablefrom E. I. DuPont de Nemours under the trade name Elvanol 71-30) wasslurried in water at 3% solids and jet-cooked at 143° C. (290° F.). Backpressure at the cooking chamber was 55 psig. The dispersed polymer wasconveyed under pressure (45 psig) through an atomization nozzle (Model1/2 J82 available from Spraying Systems Inc.) top mounted in a NiroUtility #1 spray-dryer and atomized with steam at 30 psig. Heated air at280° C. (536° F.) was used to dry the atomized solution to a freeflowing powder.

The resulting product consisted of rugose spheres generally from 3 to 6microns in diameter. A total of 31.88% of this material was soluble inwater at 25° C. (77° F.) compared to 3.6% of the unprocessed polymer.The solubility test used is the one described in U.S. Pat. No. 4,072,535(issued Feb. 7, 1987 to R. W. Short et al.). DuPont's technical servicebulletin issued December 1965 describes the PVA polymer as having"excellent resistance to cold water" and requiring elevation to 90°-95°C. (194°-203° F.) for complete dissolution in water. The viscosity ofthe spray-dried polymer at 25° C. (77° F.), dispersed in hot water at 4%solids, was 24 cps. compared to 26 cps. for the unprocessed polymer.This shows that the polymer was not substantially degraded during theprocessing.

EXAMPLE VIII

This example illustrates the use of the coupled jet-cooking/spray-dryingprocess to produce a cold-water-soluble powder from a polygalactomannangum which is normally difficult to solubilize.

Locust bean gum (available from National Starch Chemical Corp.) wasslurried in water at 1% solids and jet-cooked at 132° C. (270° F.). Backpressure at the cooking chamber was 30 psig. The dispersed gum wasconveyed under pressure (25 psig) through an atomization nozzle (Model1/2 J82) top mounted in a Niro Utility #1 spray-dryer and atomized withsteam at 30 psig. Heated air at 280° C. (536° F.) was used to dry theatomized mist to a free flowing powder.

The resulting product consisted of rugose spheres generally from 2 to 4microns in diameter. A total of 71.5% of this powdered gum was solublein water at 25° C. (77° F.) compared to 27.1% of the unprocessed gum.When redispersed in cold water at 4% solids, the viscosity was 490 cps.within 2 minutes compared to 16 cps. for the unprocessed gum. Thesolubility test referred to in Example VII was used.

EXAMPLE IX

This example describes the processing conditions used in the continuouscoupled jet-cooking/spray-drying process when starches other than highamylose starches are pregelatinized. The equipment used is described inExample I. The processing variables and results are shown in Table III.

The results show that the non-granular corn, waxy maize, and tapiocastarch powders were essentially 100% cold-water-soluble.

EXAMPLE X

This example compares the flow viscosity of jet-cooked high amylose cornstarch (about 70% amylose) to water at elevated temperatures. Highamylose starch slurries were cooked at solids of about 16.8-18.1%,cooking temperature of about 149° C. (300° F.), steam flow rate of 168g./min., and cooking rate of 59.3 ml./min. The resulting flow ratesthrough the viscometer previously described were 48, 91 and 113 ml./min.at 20, 40 and 60 psig of pressure using a 0.016 in. orifice in theatomizer nozzle. For a 0.031 in. orifice, the resulting flow rates were313-498 and 399-642 ml./min. at 40 and 60 psig. Flow rates of water,under identical conditions were 100, 138, 190, 600 and 699 ml./min.,respectively.

It can be seen that jet-cooks of high amylose corn starch flow throughthe spray-drying nozzles at rates no less than half that of water whenthe temperatures were maintained at from 126° to 153° C. (259° to 307°F.) even at 28% cook solids. This translates into a flow viscosity ofless than 1 centipoise.

In contrast, when the temperature drops after a 28% solids jet-cook ofhigh amylose corn starch exits the jet-cooker, the viscosity cannot evenbe measured as the starch cook forms a gel in a few seconds.

EXAMPLE XI

This example compares starches pregelatinized using the continuouscoupled, jet-cooking/spray-drying process with the same starchespregelatinized using the Winkler process (U.S. Pat. No. 3,630,775).

The procedure of the Winkler patent could not be exactly duplicated. Thespraying pressures disclosed in the patent range from 2000 to 6800 psigand the cooking temperatures range from 182-304° C. (360°-580° F.). Theequipment used for this experiment was limited to a pressure of 1600psig and a temperature of 160° C. (320° F.).

A B.I.F. (a division of New York Air Brake, Providence, R.I.) model 1180jacketed micro-feeder piston pump was modified to produce higher flowrates so that pressures up to 1600 psig could be achieved. Thermocoupleswere attached to the cooking chamber to monitor the temperature of thecook. The Piston cavity was filled with starch slurries at 10% to 20%solids. The slurries were heated for 20 minutes to a temperature of 160°C. (320° F.) with 100 psig of steam flowing through the jacket of thepump. The starch was then pumped through a single fluid nozzle having a0.0135 in. orifice (#80A available from Spraying Systems Inc.) at 1600psig pressure. Samples were collected and analyzed for viscosity or gelstrength.

Part A--High Amylose Starch (70% amylose)

Comparative starch samples were sprayed at 1600 psig and 160° C. (320°F.), collected, and allowed to cool and set-up for 24 hrs. at 21° C.(72° F.).

Gel strengths were run on the Texture Analyzer. Cook solids were run(using an infra-red heat lamp balance) after the gel strengths weretested.

The jet-cooking conditions used to prepare the pregelatinized starch bythe coupled process were as follows: 28% cook solids (38% slurrysolids), steam flow of 31 g./min., cooking temperature of 143° C. (290°F.), flow rate of 38.7 ml./min., and back pressure of 52 psig at thechamber and 48 psig at the nozzle. The spray-dryer used was an AnhydroDryer Model No. 1 equipped with a two fluid nozzle (set-up #22B). Theinlet temperature of the spray-dryer was 230° C. (446° F.) the outlettemperature was 84° C. (183° F.) and air at 20 psig was used foratomization.

The starches were dispersed in hot water and heated in a boiling waterbath for 15 minutes, allowed to cool and set-up for 24 hours at 21° C.(72° F.). The solids and gel strengths are shown below. The starchdegradation is shown in FIG. 3.

    ______________________________________                                                          Solids  Gel Strength                                        Sample            (%)     (g./cm..sup.2)                                      ______________________________________                                        Indirect cooking/spraying                                                                       11.1    370                                                 (comparative)     13.4    580                                                 Continuous coupled                                                                              10.3    557                                                 jet-cooking/spray-drying                                                                        13.4    768                                                 process           13.8    946                                                                   16.6    +996*                                               ______________________________________                                         *Gel strengths over 950 g are not accurate, as they are over the upper        limits of the Texture Analyzer.                                          

The results show that the high amylose starches prepared by indirectheating and pressure atomization gave lower gel strengths than the samestarch cooked and atomized by the coupled process using direct heating.This is attributed to the less effective dispersion formed duringindirect heating and the higher shear developed during atomization inthe pressure nozzle. It would be expected that pressures andtemperatures exceeding those used here, as taught in Winkler, will onlyfurther degrade the starch.

Part B--Other Starches

Comparative starch samples of waxy maize starch (about 0% amylose) andcorn starch (about 28% amylose) were sprayed at 1600 psig at atemperature of 160° C. (320° F.) and allowed to cool to 71° C. (160° F.)before viscosity measurements were taken.

Waxy maize and corn starch samples pregelatinized using the coupledprocess were spray-dried at inlet temperatures of 200° C. (392° F.) and200° C. (392° F.), and outlet temperatures of 125° C. (257° F.) and 82°C. (180° F.), using 30 psig of atomization steam and 30 psig ofatomization air respectively. The spray-dryer used for the waxy maizestarch was a Niro Utility #1 dryer equipped with a two fluid nozzle(set-up 22B nozzle and 120 cap). That used for the corn starch was anAnhydro Model No. 1 dryer with the same nozzle and set-up.

The recovered starches were dispersed in hot water and heated in aboiling water bath for 30 minutes and allowed to cool to 71° C. (160°F.) before viscosity measurements were taken. Cook solids were run(using an infra-red heat lamp balance) after all samples had beentested. The solids and viscosities are shown below. The gel strengthsare given in Part A.

    ______________________________________                                                           Solids  Viscosity                                          Sample             (%)     (cps)                                              ______________________________________                                        Waxy Maize prepared by                                                                           11.9    423                                                continuous coupled 15.6    740                                                jet-cooking/spray- 20.0    1850                                               drying process                                                                Waxy Maize         10.0     30                                                prepared by indirect                                                                             14.0     37                                                cooking/spraying   19.4    190                                                (comparative)      21.2    340                                                Corn prepared by   12.0    620                                                continuous coupled 16.3    3650                                               jet-cooking/spray- 20.4    24500                                              drying process                                                                Corn prepared by   12.0     28                                                indirect cooking/  14.0     37                                                spraying (comparative)                                                                           19.4    190                                                ______________________________________                                    

The results again show that high molecular weight starches, such asnative waxy maize and corn starch, were degraded, as shown by theextreme reduction in viscosity, when processed using indirect heatingand a pressure nozzle. The starch degradation is shown in FIGS. 4 and 5.

EXAMPLE XII

This example demonstrates that the pregelatinized, spray-dried,non-granular, amorphous high amylose starches prepared by the coupledprocess are unique. X-ray crystallographic scans (see FIG. 2) performedby Rigaku USA Danvers Mass Model No. DMAX-8 showed that thepregelatinized high amylose starch (about 70% amylose) prepared by thecoupled jet-cooking/spray-drying process was amorphous, i.e., there wereno crystalline peaks. Comparative pregelatinized starches (about 70%amylose) prepared by jet-cooking followed by drying on a heated plateunexpectedly contained crystalline regions. Samples made by jet-cookingfollowed by air-drying contained crystalline regions as expected. Nativegranular starch likewise contains crystalline regions.

The lack of retrogradation in the coupled jet-cooked/spray-driedmaterial is confirmed by the higher gel strength on redispersion (160g./cm.² at 6% solids in hot water). The same high amylose starchProcessed by jet-cooking and drum-drying had a gel strength of only 110g./cm.² on redispersion.

It is well known that retrograded starches do not provide as strong agel on redispersion below 100° C. (212° F.) compared to a more solublestarch of equal amylose content. This is due to the unavailability ofthe retrograded amylose for gel formation.

EXAMPLE XIII

Scanning Electron Microscope photomicrographs of pregelatinized highamylose (about 70% amylose) corn starches prepared by the presentcoupled jet-cooking/spray-drying process (Photograph A), thesimultaneous atomization and cooking process of U.S. Pat. No. 4,280,851(Photograph B), and the autoclaving/drum-drying process of U.S. Pat. No.3,086,890 (Photograph C) are shown in FIG. 6. The photomicrographs ofthe particles that make up the powders of these starches show distinctphysical differences.

The powders of the current invention are composed of non-granular,round, spray-dried particles having convoluted (dimpled) surfaces due tothe rapid removal of water and subsequent collapse of the starch-filmduring drying. In this process, the size of the particles are determinedby the size of the droplets formed during atomization and drying. Theseparticles are unlike those prepared by the simultaneous atomization andcooking process which are generally in the form of swollen granules.This is evidenced by the slightly wrinkled surfaces characteristic ofintact, swollen starch granules. Though a spray-dried Particle, thestarch in this photomicrograph (photograph B) was never placed intosolution and the particle size is determined largely by the degree ofgranular swelling during cooking. The powders of theautoclaving/drum-drying process are in the form of angular flakes. Theparticle size is determined by subsequent grinding and fractionation ofthe drum-dried sheet after drying.

The preparation of a spray-dried high amylose starch by the process ofthe Pitchon patent (U.S. Pat. No. 4,250,851) was difficult, and theresulting product was considerably less soluble and contained intact,non-degraded granules. As previously shown, the preparation of such astarch by the coupled process was easily carried out.

EXAMPLE XIV

This example compares the displacement density and bulk density ofvarious pregelatinized starches prepared by the present coupledjet-cooking/spray-drying process at high solids, a conventionalspray-drying process at low solids, and the jet-cooking/drum-dryingprocess similar to that of Sarko (U.S. Pat. No. 3,086,890) at lowsolids. The starches prepared by the coupled process were prepared usingsuitable processing conditions for the particular starch source.

The results in FIG. 7 show that the relationship between displacementdensity and bulk density for the various methods of preparingpregelatinized starches are specific and generally lie within regionsthat are independent of the starch source. These density differences aredue to the differences in particle shape and structure resulting fromthe drying step of each process.

Particles produced by the Sarko process are flakes which contain lessincluded air than starch powders spray-dried from dispersions; thus, thedensity of the individual Sarko process particle (i.e., displacementdensity) is higher than that of spray-dried starch powders fromdispersions. However, these angular flakes pack together lessefficiently than spheres giving a lower bulk density.

Spray-dried starch particles dried from a dispersion generally arecharacterized by internal air voids and surface ridges and depressions.This structure is formed, in the spray-dryer, as the wet atomizeddispersion droplet forms an air and water vapor filled bubble on heatingand collapses on drying. Displacement density is strongly affected bythe amount of included air which is influenced by starch type,dispersion solids, atomization variables, and spray-dryer conditions.Packed bulk density varies with particle size distribution in the powderand smoothness of the particle surface (depth of surface depressions).The coupled jet-cooking/spray-drying process yields starch powders withhigher bulk densities than conventional spray-drying when using the samehigh viscosity base starch.

These physical differences can be used to identify the process by whichthe starches were prepared when supplemented with the differences inphysical structure already discussed in previous Examples. The onlyexception in the data is the isolated potato amylose prepared by thecoupled process, which lies in region I.

    ______________________________________                                        Summary of FIG. 7                                                                                    Displacement                                                                              Bulk                                                              Density     Density                                    Process       Region   (g/cc)      (lbs/ft.sup.3)                             ______________________________________                                        Conventional jet-                                                                           I        low         low                                        cooking/spray-drying                                                          Coupled jet-  II       low         high                                       cooking/spray-drying                                                          Jet-cooking/  III      high        low-high                                   drum-drying                                                                   ______________________________________                                    

Now that the preferred embodiments of the invention have been describedin detail, various modifications and improvements thereon will becomereadily apparent to those skilled in the art. Accordingly, the spiritand scope of the present invention are to be limited only by theappended claims and not by the foregoing specification.

                                      TABLE I                                     __________________________________________________________________________    Process Conditions for Jet-Cooking/Spray-Drying                               High Amylose Starch (70% amylose)                                                           (1)  (2)  (3)  (4)  (5)                                         __________________________________________________________________________    Slurry Solids  21.0                                                                              21.5 22.0 22.5 42.5                                        Cook Solids   13.0 13.0 13.0 13.0 28.0                                        Jet Cooking Temperature                                                                     143 (290)                                                                          143 (290)                                                                          143 (290)                                                                          143 (290)                                                                          143 (290)                                   Steam Flow (g./min.)                                                                        20.0 24.0 36.0 62.0 9.25 lb./min.                               Cook Flow (ml./min.)                                                                        30.0 30.0 30.0 30.0 3.8 gal./min.                               Nozzle Type                                                                   Nozzle Set-up 22   22 B 22 B 22 B 1J-152                                      Dryer Inlet Temp °C.(°F.)                                                     220 (428)                                                                          220 (428)                                                                          220 (428)                                                                          220 (428)                                                                          239-191                                                                       (446-375)                                   Dryer Outlet Temp °C.(°F.)                                                    82 (180)                                                                           82 (180)                                                                           82 (180)                                                                           82 (180)                                                                           82-96                                                                         (180-205)                                   Atomizer Air (psig)                                                                         20.0 20.0 20.0 20.0 120.0 (steam)                               Gel Strength (g./cm..sup.2)                                                                 194.0                                                                              215.0                                                                              204.0                                                                              134.0                                                                              200.1                                       __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________    Process Conditions for Jet-Cooking/Spray Drying                               Various High Amylose Corn Starch                                                               Fractionated          Fluidity High Amylose Corn                              Potato Amylose                                                                           High Amylose Corn                                                                        (about 70% amylose; about                               (about 100% amylose)                                                                     (about 50% Amylose)                                                                      25 CaCl.sub.2 viscosity)               __________________________________________________________________________    Slurry Solids    20.0       26.7       30.0                                   Cook Solids      12.5       16.0       21.0                                   Jet Cooking Temperature °C.(°F.)                                                 154 (310)  143 (290)  143 (290)                              Steam Flow (g./min.)                                                                           27.5       27.5       27.5                                   Cook Flow (ml./min.)                                                                           19.9       27.0       39.7                                   Nozzle Type      2 FLUID    2 FLUID    2 FLUID                                Nozzle Set-Up    22 B       22         22                                     Dryer Inlet Temperature °C.(°F.)                                                 225 (437)  230 (446)  220 (428)                              Dryer Outlet Temperature °C.(°F.)                                                86 (187)   85 (185)   88 (190)                               Atomizer Air (psig)                                                                            40.0       20         20.0                                   Cold Water Solubility (%)                                                                      86.6       95.3       93.0                                   Hot Water Solubility (%)                                                                       99.2       96.9       97.1                                   Gel Strength (g./cm..sup.2)                                                                    395        125        104                                    __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________    Process Conditions for Jet-Cooking/Spray-Drying                               Other Starches                                                                               Corn Starch                                                                          Waxy Maize Starch                                                                       Tapioca Starch                                __________________________________________________________________________    Slurry Solids  20.0   20.0      20.0                                          Cook Solids    14.0   14.2      11.0                                          Jet Cook Temperature °C.(°F.)                                                  143 (289)                                                                            152 (305) 160 (320)                                     Steam Flow (g/min)                                                                           35.0   31.0      47.0                                          Cook Flow (ml/min)                                                                           20.5-28.8                                                                            18.9-21.2 11.3-16.9                                     Nozzle Type    2 FLUID                                                                              2 FLUID   2 FLUID                                       Nozzle Set-Up  22 B   22 B      22 B                                          Dryer Inlet Temp °C.(°F.)                                                      225 (437)                                                                            225 (437) 218 (424)                                     Dryer Outlet Temp °C.(°F.)                                                     86 (187)                                                                             97 (207)  95.0 (203)                                    Atomizing Air PSI                                                                            20-25  25.5      15.0                                          Moisture (%)   5.0    5.6       5.0                                           1% Solids pH   6.5    6.8       6.9                                           Cold Water Solubility (%)                                                                    98.6   97.7      100.0                                         __________________________________________________________________________

What is claimed is:
 1. A pregelatinized, spray-dried, non-granularstarch powder of a modified starch base having an amylose content ofabove about 40%, pregelatinized by a coupled, continuousjet-cooking/spray-drying process, and characterized in that the starchis substantially non-crystalline and substantially non-retrograded andhas a bulk density higher than the bulk density of the same base starchpregelatinized by jet-cooking and spray-drying in two separate steps. 2.A pregelatinized, spray-dried, non-granular starch powder of a modifiedstarch base containing amylose in an amount of up to about 40%,pregelatinized by a coupled, continuous jet-cooking/spray-dryingprocess, and characterized in that the starch is substantiallynon-crystalline and has a bulk density higher than the bulk density ofthe same base starch pregelatinized by jet-cooking and spray-drying intwo separate steps.
 3. A pregelatinized, spray-dried, non-granularstarch powder which comprises a mixture of a pregelatinized,spray-dried, non-granular starch powder of a modified starch base havingan amylose content of above about 40% and a pregelatinized,non-granular, spray-dried starch powder of a modified starch basecontaining amylose in an amount of up to about 40%, the starch powderspregelatinized by a continuous coupled jet-cooking/spray-drying process,and characterized in that the starch powders are substantiallynon-crystalline and have bulk densities higher than the bulk densitiesof the same base starches pregelatinized by jet-cooking and spray-dryingin two separate steps, and further characterized in that the modifiedstarch base having the amylose content of above about 40% issubstantially non-retrograded.
 4. A mixture of (a) a pregelatinized,spray-dried, non-granular starch powder pregelatinized by a continuouscoupled jet-cooking/spray-drying process and (b) a fully pre-dispersed,jet-cooked/spray-dried gum; characterized in that the pregelatinizedstarch powder is substantially non-crystalline, has a bulk densityhigher than the bulk density of the same starch pregelatinized byjet-cooking and spry-drying in two separate steps, and is substantiallynon-retrograded when the starch has an amylose content of above about40%; and characterized in that the pre-dispersed gum iscold-water-dispersible.
 5. A fully pre-dispersed, jet-cooked/spray-driedlocust bean gum which is cold-water-dispersible.
 6. A fullypre-dispersed, jet-cooked/spray-dried, substantially fully hydrolyzedpolyvinyl alcohol which is cold-water-dispersible.